Judge Morris asked, "How did they use his car without the keys?"
Ms Pearson said others knew where the keys were kept and it was "entirely possible someone used those keys and used his vehicle, and put them back before he awoke".
She said this "seems to be accepted by police in their summary".
Smith had later been pulled over by police "on an unrelated matter", and the sawn-off weapons were found.
Ms Pearson said Smith had pleaded guilty on the basis he knew the weapons were there.
"He was aware but chose to be ignorant of the fact they were there," Ms Pearson said. "He didn't know, he didn't want to know. The place he was at, ignorance was an easier option."
Judge Morris asked police prosecutor Sergeant Neill Ford for the police view on a probation report that recommended a community work sentence.
Mr Ford said community detention should be the bare minimum sentence because he "had known they'd been in the boot at least 10 days".
The judge said there was "no question that if someone possesses such a weapon for their own purposes", a sentence of about two-and-a-half years in prison was likely.
"The only reason people cut down rifles like this is to commit serious offences such as aggravated robbery."
Judge Morris said someone had borrowed Smith's car and left the firearms in it, and "when you became aware of them, you "froze".
She told him, "there is a real obligation on those come across such weapons to ensure they are nowhere near them, and clearly not to keep them for 10 days."
